Aoi Mizusawa, Ren Homura's classmate, serves as the catalyst for his entry into real-world monster battles. After aiding Ren during his first confrontation, she supplies him with a specialized ring crucial for controlling monsters outside the game and orchestrates his recruitment into her former Monster Strike team. Her primary associated monsters are Fox Metal the Legend and Napoleon the Valiant.

Her surname, Mizusawa, derives from Japanese words for "water" (水) and "marsh" (澤), while her given name, Aoi, signifies "hollyhock" or "althea" (葵).

She maintains a consistent presence across franchise installments. As a main character, she features in the primary series, the film *Monster Strike The Movie: Hajimari no Basho e*, the ONA *Rain of Memories*, the special *An Encore and Continuance - Pandora's Box*, and *Monster Strike: Katsubou no Hate no Risoukyou*. In a supporting role for *Monster Strike: Mermaid Rhapsody*—a summer special set between Episodes 35 and 36 of the first season—she accompanies Ren, Minami, and others to Okinawa on Minami's father's trip, though her specific actions during the beach-related mysterious events remain undetailed. She also appears supportingly in *Monster Strike Anime: Kieyuku Uchuu-hen*.

Throughout the second season, she continues as a core group member alongside Ren, Akira Kagetsuki, Minami Wakaba, and transfer student Mana, addressing disruptions from monsters manifesting beyond the game's confines.